/un'deuhr luy"/ , v.t. underlay, underlain, underlying .
1. to lie under or beneath; be situated under.
2. to be at the basis of; form the foundation of.
3. Gram. to function as the root morpheme or original or basic form of (a derived form): The form "boy" underlies "boyish."
4. Finance. to be primary to another right or security.
[ bef. 900; ME underlyen (v.), OE underlicgan. See UNDER-, LIE 2 ]